Field of the Invention
In a turbocharger the shaft is typically sealed with respect to the bore of the bearing housing at the turbine wheel end by one or more shaft seal rings (or piston rings) which sit in annular grooves provided in the shaft behind the turbine wheel. Problems can arise with this conventional shaft seal arrangement where the turbocharged engine has an engine brake valve located downstream of the turbine. As the engine brake is activated, the back pressure in the exhaust line, and thus in the turbine wheel housing, rapidly rises and can reach 7 bar. The inventive shaft seal design makes it possible to assemble a seal with ring seals with higher wear resistance and thus to maintain the seal's effectiveness over heavy use.
Description of the Related Art
Turbochargers use the exhaust flow from the engine exhaust manifold, which enters the turbine stage of the turbocharger at a turbine housing inlet, to drive a turbine wheel, which is located in the turbine housing. The turbine wheel is affixed to one end of a shaft that is rotatably supported within a bearing housing. The shaft drives a compressor wheel mounted on the other end of the shaft. The turbine wheel, shaft and compressor wheel form a rotating assembly that is supported within the bearing housing. As such, the turbine wheel provides rotational power to drive the compressor of the turbocharger. This compressed air is then provided to the engine intake at a greater density than would be possible in a normal aspirated configuration. This allows more fuel to be combusted, thus boosting the engine's horsepower without significantly increasing engine weight.
When a commercial truck, equipped with an engine compression type exhaust brake, travels down a grade with a long incline, the exhaust brake can be used to block the flow of exhaust gas downstream of the turbine wheel and provide retardation to the vehicle, independent of the vehicle's wheel brakes. The mass and inertia of the truck rolling down the incline forces rotation of the engine through the vehicle gearbox which is driven by the wheels. With no fuel being introduced into the engine, the engine acts like an air pump against the blockage of the exhaust brake, consuming energy and retarding the velocity of the truck.
The turbocharger shaft is typically sealed with respect to the bore of the bearing housing at the turbine wheel end by shaft seal rings (or piston rings) which sit in an annular grooves provided in the shaft behind the turbine wheel (see, e.g., BorgWarner WO2014099289, FIG. 2). The shaft seal prevents oil from the bearing lubrication systems from leaking into the turbine housing which can cause blue smoke and oil drips from the exhaust pipe, as well as preventing exhaust gas pollution of the bearing housing which can cause overheating and adversely effect bearing life.
Problems can arise with this conventional shaft seal arrangement upon activation of the engine brake valve located downstream of the turbine. As the engine brake is activated the back pressure in the exhaust line, and thus in the turbine wheel housing, rapidly rises and can reach 7 bar. As pressure behind the turbine wheel increases, the shaft seal ring(s) can be pushed inboard. This movement, together with the high rotational speed of the shaft, can generate excessive frictional heating which can cause the shaft seal ring to overheat. This in turn can cause the rings to be more susceptible to movement in the bore and induce a rapid failure of the seal.
It is an object of the present invention to overcome the above problem.